1. Field of the Invention
The present invention generally relates to hand tools and, more specifically, to a front-loading adjustable safety utility knife with safety utility knife with safety quick-release lock.
2. Description of the Prior Art
Utility knives are widely used in construction, business and hobby applications for cutting such materials as paperboard, wallboard, string and other objects. Commonly, such utility knives are in the form of an elongate hollow housing that can be gripped by the user along an intermediate portion thereof and into which there are placed trapezoidal flat cutting blades. The blades typically have a single cutting edge. The blade is typically slidably mounted on a carrier for movement between a retracted position within the housing and an extended position in which the cutting edge is at least partially exposed through a front end aperture or slot, the carrier being coupled to a manually operated element, such as a button positioned in a manner convenient to be actuated by the user""s hand.
Many utility knives include a region within the housing for storing one or two additional blades that can be used to replace the operative blade when it becomes dull. In most cases a screw or similar means is used for attaching the two clam shell members together during normal use. When blades are to be replaced, the screw is removed, allowing the two shell members to be separated, and access is provide to the replacement blades.
A number of utility knife designs have been proposed that facilitate the removal, reversal or replacement of blades without separating the mating handle parts or shell members. Thus, in U.S. Pat. No. 3,845,554, a knife blade and handle are disclosed in which a leaf spring is mounted in the holder that supports projecting pins which are adapted to enter into two openings or notches in the blade. The leaf spring is manually movable between a blade clamping and a blade release position. However, with this design, when the handle parts are separated for any reason, the mechanical parts or components which position and move the blade can themselves be separated from and be dislodged from the handle, making it possible for these parts to be misplaced. The user must replace all the parts in their original positions prior to reassembly of the handle. This may be difficult and inconvenient due to the presence of a loose compression spring which is itself held in position by the leaf spring.
In U.S. Pat. No. 5,168,630, a blade carrier tool is disclosed which has a somewhat complicated construction in which a jaw partially pivots away under the control of a separate release mechanism provided at the rear of the handle to partially expose the blade. This release mechanism occupies a significant amount of space within the handle, rendering that space useless for storage of additional blades. The blade must additionally be manipulated in order to release the blade from the blade-retaining elements because of the small extent to which the jaw pivots to provide limited access to the interior of the tool. Also, in U.S. Pat. NO. 5,495,670, a utility knife is disclosed which includes a pivoted access panel which can be pivoted open to provide access to the front blade. However, the opening of this panel essentially releases the blade, which may drop out of the utility knife, there being nothing to retain the blade once the panel opens. This may create an unsafe condition if the blade falls out and the user tries to catch it with the user""s hand.
In U.S. Pat. No. 5,644,843, a utility knife is disclosed which allows the active or operative blade to be lowered below the housing by controlling the position of a blade carrier. However, as in the previously mentioned patent, once the blade carrier is lowered below the knife handle, the blade is susceptible of being dislodged and falling out of the unit. Additionally, in this patented design, the same manually actuated button is used to slide the blade outwardly to the operative position as well as to release the blade. This may result in inadvertent movement of the button to a release position when such was not intended. By providing a design in which the blade can be dislodged with a singlehanded operation, there is the danger that the blade will be inadvertently dislodged, and injury to the user may result.
Accordingly, it is an object of the present invention to provide an adjustable safety utility knife which does not have the disadvantages inherent in known utility knives.
It is another object of the present invention to provide an adjustable safety utility knife which is simple in construction and economical to manufacture.
It is still another object of the present invention to provide a safety utility knife as in the previous objects which facilitates the insertion, reversing and replacement of the cutting blade.
It is yet another object of the present invention to provide an adjustable safety utility knife as in the present invention which allows simple and convenient insertion, reversal and replacement of a cutting blade through the front opening or aperture without the need to separate the clam shell members forming the handle of the knife.
It is a further object of the present invention to provide an adjustable safety utility knife which is safe and convenient to use and minimizes the probability that the user will be exposed to a blade that inadvertently falls out of the knife.
It is still a further object of the present invention to provide an adjustable safety utility knife which provides a carriage for transporting the cutting blade that can conveniently and safely release a blade for movement through the front aperture and which is in the form of a unitary assembly that incorporates springs and other components that can be inserted and removed from the knife as an unit or sub-assembly.
In order to achieve the above objects, and others which will become apparent hereinafter, an adjustable safety utility knife in accordance with the present invention comprises an elongated ergonomically shaped handled formed of two elongate shell members, each having a peripheral edge and an outer convex surface and an inner generally concave surface. Fastening means is provided for fastening such shell members at said peripheral edges along a vertical parting plane to form an elongated internal cavity. Said handle defines a front end, a back end and an intermediate portion suitable for being gripped by a user and also defining top and bottom surfaces extending along opposite sides of said front end substantially aligned with said parting plane and dimensioned for passage of a flat cutting blade therethrough. Guide means is provided within said elongated cavity for guiding the cutting blade between a first position for safely storing the blade fully inside said cavity and a second position for selectively extending the blade beyond said aperture to expose at least a portion thereof. A manually operated button is arranged on said top surface and coupled to said guide means for selectively moving the blade between said first and second positions.
Said guide means includes a carriage within said elongated internal cavity for supporting a flat cutting blade and guide elements are provided on at least one of said inner generally concave surfaces for guiding said carriage or cutting blade carrier between said first and second positions. Said carriage includes locking means for normally locking a cutting blade mounted thereon to substantially fix the cutting blade against relative longitudinal movements between said cutting blade and said carriage. Said locking means also includes an unlocking element, the actuation of which releases a cutting blade to permit relative longitudinal movements between said cutting blade and said carriage. Blade release means is provided on one of said shell members for actuating said unlocking element when manual force is applied thereto. Therefore, application of a force on said blade release means releases said cutting blade and enables it to be withdrawn through said end aperture.